Closed loop engine control system

ABSTRACT

A closed loop engine control system for internal combustion engines is described. The control system is responsive to signals indicative of the presence or absence of oxygen in the exhaust gas of the engine and is operative to generate an output signal for receipt by a fuel delivery controller which will cause that fuel delivery controller to increase fuel delivery in the presence of oxygen molecules in the exhaust gas and to decrease fuel delivery in the absence of oxygen molecules in the exhaust gas in order to maintain the fuel delivery at the predetermined, and preferably the stoichiometric, air/fuel ratio mixture point.

[111' 3,815,561 1451 June 11, 1974 CLOSED LOOP ENGINE CONTROL SYSTEMInventor:

[75] William R. Seitz, Farmington, Mich.

The Bendix Corporation, Southfield, Mich.

Sept. 14, 1972 Assignee:

Filed:

Appl. No.:

References Cited UNITED STATES PATENTS 5/1936 Morgan 60/276 2/1945Millenborg 60/276 l/1968 McKenzie 60/39.28 R 10/1968 Sano 12/1970Howland 9/1971 lO/l97l lO/l972 3,707,950 I 1/1973 3,724,430 4/19733,738,341 6/1973 3,745,373 7/1973 3,745,768 7/1973 3,759,232 9/19733,782,347 l/l974 FOREIGN PATENTS OR APPLICATIONS 600,895 4/1948 GreatBritain 60/276 Primary ExaminerDouglas Hart Attorney, Agent, orFirm-Robert A. Benziger; Gerald K. Flagg [57] ABSTRACT A closed loopengine control system for internal combustion engines-is described. Thecontrol system is responsive to signalsindicative of the presence orabsence of oxygen in the exhaust gas of the engine and is operative togenerate an output signal for receipt by a fuel delivery controllerwhich will cause that fuel delivery controller to increase fuel deliveryin the presence of oxygen molecules in the exhaust gas and to decreasefuel delivery in the absence of oxygen molecules in the exhaust gas inorder to maintain the fuel delivery at the predetermined, and preferablythe stoichiometric, air/fuel ratio mixture point.

11 Claims, 7 Drawing Figures COMPARATOR y FUEL DELIVERY CONTROLLER.

7o- SET POINT ENGINE INPUTS ;/0 r60 EXHAUST OXYGEN SENSOR ENGINEPATENTEDJUM 1 m4 SHEEI 10F 3 ENGINE INPUTS R R Em 0 m m L E 0) W x m D 60 N LC E E U F T m a T A22 m um m 0E T 2 I. E x S R R w 0 N m s R S m wm c m X 0 FIG. I

FROM oxvsem SENSOR TO oxvssu SENSOR 6ND PATENTEDJUHI 1 1974 SHEEI 2 OF 3TB+ I /2/ I I FIG. 3

SENSOR VOLTAGE SIGNAL PATENIEDJUN 1 1 m4 1 3,8 SL561 SHEET 30F 3 FIG.4[0v 2 i STOICHIOMETRIC INCREASING AIR/FUEL RATIO 5 SET POINT VALVE vINCREASING 83 v '5v COMPARATOR INPUT SIGNAL I! g 8 U FIG? FUEL DELIVERYCOMMAND PULSES l I CLOSED LOOP ENGINE CONTROL SYSTEM BACKGROUND OF THEINVENTION' 1. Field Of The Invention The present invention is related tothe field of internal combustion engine control systems in general andin particular to that portion of the above noted field concerned withclosed loop control systems. In greater detail, the present invention isconcerned with a closed loop control system in which the exhaust gasesof an internal combustion engine are analyzed to indicate the ratio ofthe air/fuel mixture being consumed by the engine and through whichsignals are generated in order to modulate the fuel delivery mechanismin order to provide a predetermined air/fuel ratio mixture for theengine.

2. Description Of The Prior Art Closed loop fuel control systems arewell known in the internalcombustion engine art, in particular in thatportion of the internal combustion engine art which is devoted to thehot gas turbine engine, to provide short term and long term inputcontrol corrections. However, as applied to variable volume combustionchamber type engines, such as the reciprocating piston or rotary(Wankel) engine, closed loop fuel control systems are not well known.One known system involves the use of an exhaust gas oxygen concentrationsensor one example of which is described in co-pending commonly assignedpatent application Ser. No. 284,386 filed Aug. 28, 1972 by Thomas .I.I-Iemak and titled Protective Shield for Oxygen Sensor." This systemrelies upon the virtual step function output signal of the oxygenconcentration sensor (as illustrated in FIG. 4) to directly effect thefuel delivery control mechanism to increase or decrease the volume offuel delivered as a function of air being consumed by the engine withthe magnitude and speed of the correction being a function of the sensoroutput signal. In working with a closed loop fuel control system basedon this sensor it has been observed that the sensor output signalcharacteristic varies greatly as a function of sensor temperature andalso as a function of sensor age. While the sensor output characteristicnormally evidences a high to low transition at the stoichiometricair/fuel mixture ratio point, the magnitude of this transition (andhence the magnitude of the output signal) decreases for an aging oxygensensor and also is a direct function of sensor temperature asillustrated in FIG. 4. This results in a closed loop control systemwhichis least effective during the engine'warm-up cycle and until the sensorreaches its normal operating temperature. Since accurate fuel controlduring the warm-up cycle is known to be important in reducing automotiveexhaust emissions it is therefore an object of the present invention toprovide a closed loopcontrol system capable of examining engine exhaustand controlling fuel admission to the engine which is not sensitive totemperature induced variations in the sensor output signal. Moreparticularly it is an object of the present invention to provide such aclosed loop control system which is fully responsive to sensor outputsignal variations having a minimal magnitude. In this context. minimalmagnitude is to be understood to mean a signal magnitude of aboutpercent of the maximum signal magnitude. It is also an object of thepresent invention to provide a closed loop control system whoseresponsiveness is not altered by degradation of the sensor device.

Closed loop controls for variable volume combustion chamber internalcombustion engines. utilizing the known oxygen sensors provide acorrective signal which is directly related to the sensor output signal.However, as the sensor ages, the magnitude of its-output signaldecreases so that the closed loop control response time will begradually slowing therebyresulting in a long term decrease in theresponsiveness of the closed loop control system rendering the knownclosed loop controls to beof little value. It is therefore a furtherobject of the present invention to provide a closed loop control systemwhose output performance is not altered or affected by age-inducedchanges in the sensor signal. It is a more particular object of thepresent invention to provide a closed loop control system which givesuniform response without regard to variations in the magnitude of theinput signal. It is a still further object of the present invention toprovide a closed loop control system which provides uniform responsewithout regard to age or temperature of the sensor SUMMARY OF THEPRESENT INVENTION I have determined that the typical sensor outputsignal, regardless of the sensors age or operating temperature, willmake a high-to-low or a low-to-high signal excursion through at leastone intermediate sensor output signal voltage value which may be termedthe transitional value." In some instances, a sensor may have atransitional band, comprised of a plurality of output signal values eachof which could be a transitional value. That is to say, that the maximumlow signal voltage value is less than the minimum high signal voltagevalue and that between these two voltage values there exists a nominalsensor output voltage value excursions through which may advantageouslybe used to trigger a comparator circuit so that whenever the sensoroutput signal is greater than the transitional value, the comparator.will generate an output signal having a first predetermined constantmagnitude which magnitude will be uneffected by variations in sensortemperature-or age. Furthermore, whenever the sensor output signal isbelow the transitional value, the comparator will generate an outputsignal having a second predetermined constant magnitude different fromthe first predetermined magnitude which again will not be influenced bysensor, temperature or age. Thus, the

comparator output signal may be applied to the fuel delivery controllerto increase or decrease the quantity of fuel in the air/fuel mixturebeing provided to the inter nal combustion engine in response to thesensor signals. This system will therefore be rendered insensitive tovariations which may be due to variations in the temperature of thesensor or which may result from aging of the sensor.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates the closed loopcontrol system of the present invention in a blockdiagram.

FIG. 2 illustrates an electronic circuit which may comprise a portion ofthe block diagram of FIG. 1.

FIG. 3 illustrates an electronic circuit which may receive the outputsignal of the circuit of FIG. 2.

FIG. 4 illustrates various voltage signal waveforms which may beproduced by the oxygen sensor of FIG.

t 3 l in response to variations in sensor temperature and- /or age.

FIG. 5 illustrates the voltage output signal generated by the comparatorof FIG. 1.

FIG. 6 illustrates a full cycle of the voltage waveform as a function oftime generated by the circuit of FIG. 3 to control fueldelivery. v i

, FIG. 7 illustrates the output signal generated by the circuit of FIG.3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG.1, a block diagram of a closed loop control system according to thepresent invention and intended for association with a variable volumecombustion chamber internal combustion engine 10 is illustrated. Theengine 10 produces an exhaust gas stream through conduit 12 which streamis examined by an exhaust sensor 20. The presently preferred embodimentcontemplates an oxygen sensor operativeto determine the percentage ofoxygen concentration present within the exhaust gas stream. According tothe prior art this oxygen sensor would provide a virtual step functionoutput signal to be applied directly to a fuel delivery controller 50.However, according to the present invention, the output signal of theoxygen sensor is applied to a summing device which also receives thefixed value signal, termed the set point value. The out-. put of thesumming device 30.is then applied to comparator means which generates anoutput signal hav ing a first relatively low fixed value when the outputof the oxygen sensor 20 exceeds the set point value and a secondrelatively high fixed value when the output of the oxygen sensor 20 isless than the set point value. This output signal is applied to the fueldelivery controller -to influence or modulate the amount of fuel beingprovided to the engine 10. The engine 10 receives various control inputsas illustrated at which may be for example an air consumptioncontrolling input in the form of a throttle setting (which may beoperator controlled) as well as other inputs which may or may not becontrolled such as the load placed upon the engine, ignition advance orretard signals or modulation of exhaust gas recirculation (EGR). Thefuel delivery controller 50 also receives intelligence via communicationlink which is indicative of the moment-tomoment operation of the engine.For example, in the known fuel injection systems, this intelligence maycomprise information as to the speed of the engine, the temperature ofthe engine coolant, the density of the air being consumed by the engine,and such other input information as may be of use to the fuel deliverycontroller 50 in providing a gross fuel delivery control. The fueldelivery controller 50 would then control the quantity of fuel to bedelivered to the engine through conduit in accordance with these varioussensed parameters. The closed loop control would be operative tomodulate the gross fuel delivery control signal in accordance with acorrection factor determined by oxygen sensor 20. In this manner, thesystem will automatiwould directly or indirectly effect the quantitiesof air and/or of fuel being measured, computed or delivered.

Referring now to FIG. 2, the summing device 30 and the comparator 40 areillustrated in a representative, and preferred, electronic embodiment.The summing device 30 is comprised of a pair of interconnected resistors32, 34'with the resistor 34 arranged to-receive the output signal fromthe exhaust sensor 20'and resistor 32 arranged to receive a fixed valuevoltage signal from potentiometer 36. Resistors 32, 34 areinterconnected at circuit location 38. Circuit location 38 communicateswith one input to an operational amplifier 42. The other input to theoperational amplifier 42 is communicated to a fixed voltage referencewhich represents the set point value. Oppositely directed diodes 44, 45provide a feedback path around operational amplifier 42 to establishmaximum and minimum output signal levels. In the illustrated embodimentthe fixed voltage reference is established by communicating anonregulated source of voltage B+ through a resistance 41 to the cathodeof a zenner diode 43 whose anode is communicated to ground. This sourceofregulated voltage is also applied to the potentiometer 36 of thesumming device 30 and to the oxygen sensor to establish a referencevoltage or middle ground at the oxygen sensor. This will permit theoxygen sensor to generate an output signal which is referenced to themiddle ground value so that, in the application of the present inventionto an automotive vehicle which uses a dc. supply with chassis ground(positive or negative) an intermediate voltage value will be used by theoxygen sensor as its ground in order to provide both positive andnegative voltage values (relative to the middle ground) for theamplifier 42. The potentiometer 36 should be adjusted so that circuitlocation 38 will be at a voltage value equivalent to the referencevoltage established by zenner diode 43, the set point value, when theoutput from the oxygen sensor 20 .is at the transitional value. That is,the set point value should be selected to correspond to the selectedtransitional value of the exhaust'sensor. Alternatively, a voltagedivider may be used in place of potentiometer 36 where adjustability isnot required.

With reference to FIG. 4, a graph is shown illustrating the outputsignal characteristic of the typical oxygen sensor with three outputsignal characteristic curves shown demonstrating a high to low excursionat the stoichiometric air/fuel mixture .ratio. The curve identified as 1corresponds to the maximum output signal excursion which would beproduced by a new sen sor operating at its maximum operatingtemperature. Curves 2 and 3 are illustrative of the output signalcharacteristic evidenced by an oxygen sensor operating at successivelycooler temperatures or which is successively older. The signal curve 1evidences a maximum excursion which, for way of example, would go froman output signal value of approximately 1.0 volts to an output signalvalue of 0.1 volts for increasing air/fuel ratio with the excursionoccurring substantially at the stoichiometric mixture ratio. Extremeaging of the device or operation of the device at a temperature farbelow its normal operating temperature will result in a minimal signalexcursion of about 0.2 volts. In the case of the sensor whose outputsignal characteristics are here illustrated, the signal characteristicsof the curves 1, 2, and 3 overlap for a narrow region of output signal(of about 0.05 volts) centered at a value of about 0.5 volts as thevarious signals demonstrate their excursion characteristic. Thetransitional band for this sensor is thus about 0.05 volts wide and anominal value of 0.5 volts may be selected as the representativetransitional value. The set point value would then be selected tocorrespond to the transitional value of 0.5 volts.

FIG. 5 illustrates the output of comparator device 40. The comparatordevice output signal demonstrates a minimum to maximum excursion of from0.7 volts to +0.7 volts for increasing values of the sensor outputsignal with the excursion occurring when the sensor output, signalequals the set point value, in this instance 0.5 volts. Thus, the outputof the comparator device will be independent of time based variations inthe sensor output signal, due for example to sensor aging, and will alsobe independent of temperature band variations in the sensor outputsignal so long as the minimum sensor signal excursion is occurring andis passing through the selected transitional value.

Referring now to FIG. 3, an electronic circuit is illustrated whichaccomplishes the general functions of the fuel delivery controller 50.The illustrated circuit includes a major portion of the electronic'fuelinjection computer according to copending commonly assigned patentapplication, Ser. No. 226,498 filed on Feb. 15, 1972 issued May 23, 1973as US. Pat. No. 3,734,068 in the name of J1 N. Reddy and titledElectronic Fuel Control System Including Electronic Means For ProvidingA Continuous'Variable Correction Factor and is intended to beillustrative of one method for modulating fuel delivery in response tomodulation commands of'a closed loop control. The circuit of this figureis comprised of a pair of current sources 101, 102 which are alternatelyapplied to a pair of timing capacitors 103, 104 by a switching network105. receiving triggering signals at terminals 51, 52. Alsoreceivingtriggering signals at terminals 51, 52 (separately shown forconvenience) network 106 controls the level of the voltage on theselected capacitor 103, 104 prior to generation of the injection commandsignal. Threshold establishing circuit means 107 samples the highestvoltage appearing across capacitors 103, 104 and compares this valuewith the level established by the signal received at input port 53 tocompute the fuel injection command signal. This signal may be derived byvarious known techniques such as illustrated in the co-pending Reddyapplication.

The current source 101' is comprised of transistor 108 whose base isconnected to the junction of a pair ment is operative to establishreadily calculable levels of'current flow in the collectors oftransistors 108, 109, respectively. The collector of transistor 108 isthen connected in a parallel fashion to the collectors of a pair oftransistors 131, 132. Similarly, the collector of transistor 109 isconnected in parallel to the collectors of a pairof transistors 133,134. The bases of transistors 131 and 134 are connected together throughresistances 141, 142 while the bases of transistors 132, 133

are connected by way of resistances 143, 144. The junction ofresistances 141, 142 is connected to terminal 51 while the junction ofresistances 143,144 is connected to terminal 52. The emitters oftransistors 131 and 133 are connected to capacitor 103 while theemitters of transistors 132 and 134 are connected to capacitor 104. Thiscircuit is arranged to provide the current flow from current source 101through transistor 13] to capacitor 103 and the current from source 102through transistor 134 to capacitor 104 whenever a high voltage signalappears at terminal 51 and alow voltage signal appears at terminal 52.Whenever a low voltage signal is present at terminal 51 and a highvoltage signal is present at terminal52, the current from source 101will flow through transistor 132 to capacitor 104, while the currentfrom source 602 flows through transistor 133 to capacitor 103 Thethreshold establishing circuit receives a signal indicative of, forexample, an engine operating parameter such as the manifold pressure atterminal 53 and this signal is applied to the base of transistor 172.The base of transistor 171 receives, by way of diodes 161, 162, thesignal from the one of capacitors 103, 104 whose accumulated charge, orvoltage, is highest. As the emitters of transistors 171, 172 arecoupledtogether, one of these transistors will be in conductiondepending upon which has a base residing at a higher voltage value. Whenthe value appearing on the base of transistor 171 exceeds the valueappearing on circuit input 170, transistor 171 will go into conductionand transistor '1 72 will drop out of conduction. Termination ofconduction of transistor 172 will consequently terminate conduction oftransistor 173. While transistor 172 was conducting, transistor 173 wasalso conducting and a relatively high voltage signal, as illustrated inFIG. 7, was present at terminal 54 due to the voltage divider action ofresistors 182, 183. However, termination of conduction of transistor 173will result in a substantially zero or ground level signal appearing atcircuit location 174 due to the lack of current flow through theresistors 182, 183. This output signal may be applied to any of theknown injector valve driver circuits one of which is illustrated in Ser.No. 130,349

Junuthula N. Reddy Control Means For Controlling The Energy Provided ToThe Injector Valves Of An Electronically Controlled Fuel System toconstitute an injection command signal.

The timingcapacitor discharging and initial charge controlling circuitry106 is comprised of a plurality of reference level establishing means210, 212, and 214, a pair of discharging means 216, 218, switching means220 and a current source means 222. The reference level establishingmeans 210, 21 2, and 214 are connected to the source of energy indicatedas 3+ and are comprised of voltage dividermeans 224, 226, and 228,respectively, and voltage signal communicating transistor means 230,232, and 234 respectively; The voltage communicating transistor means230, 232 and 234 are arranged to have their bases communicated to aportion of the voltage divider means so that a known level of voltagemay appear thereon and their emitters are connected to a common point.The collectors of the transistors 230 and 232 are coupled together andare communicated to ground through a diode means 236 while the collectorof transistor 234 is communicated to ground through a separate diodemeans 238. The

collector/diode junction of the transistors 230, 232 and 7 diode means236 is communicated to the discharging means 216 while thecollector/diode junction of transistor 234 and diode means-238 iscommunicated to the discharging means 218.

With reference to FIG. 6, a complete cycle of a voltage waveform on thecapacitors 103, 104 is illustrated. The portion of the wave from a to frepresents the voltage attributable to the current I from source 101while the portion identified as 4 represents the portion attributable tothe current l from source 102. The various level changes and slopespresent in the I initial portion of the waveform are attributable to theaction of the reference level establishing means 210, 212,- 214 and thecharging and discharging characteristics of the capacitors under theinfluence of the current I and the discharging means 106, 216, 218. Asimilar wavefrom 180 degrees out of phase with this waveform isgenerated on the other of the capacitors 103, 104 so that the initialpoints a and f of the first and second portions of the waveforms on thecapacitors 103, 104 coincide in timeand also coincide with the receiptof mutually exclusive triggering signals received on terminals 51, 52.Receipt of a relatively high signal at terminal 51 will result in arapid dumping of the energy stored in capacitor 103 and the resultantapplication of current 1 to the capacitor 103 to charge that capacitor.The voltage appearing on that capacitor as a result of the applicationof current I and as modulated by the action of the reference levelestablishing means 210, 212 will result in a voltage waveform appearingon capacitor 103 substantially as shown in FIG. 6 from points a throughb, c, d, e and to point f on the curve in FIG. 6. At the point in timecorresponding to point f, the triggering inputs received at inputterminals 51, 52 will be reversed so that capacitor 103 will receive thecurrent 12. The value of current I2 will be a function of the voltageappearing on the base terminal of transistor 109 and will chargecapacitor 103 as shown on the portion of the curve identified as 4 ofFIG. 6. A representative threshold value is illustrated in FIG. 6 as thedashed line and the second portion of the curve, 4, crosses thethreshold -5 at a point in time identified as T1,. The circuit of FIG. 3would therefore be operative to provide a flow of fuel to the engines inaccordance with the teachings of the abovenoted pending applications forthe time period between T and T With reference now to FIG. 3, modulatingnetwork or means 118 is illustrated as communicating with the base oftransistor 109 through resistance 119. As illustrated, the modulatingmeans 118 is comprised of an operational amplifier 120 having acapacitor 121 in its feedback loop communicating with the invertinginput which also communicates through resistor 122 with a terminal 123.This terminal communicates directly with a similarly designated terminalof the comparator device 40 of FIGS. 1 and 2. Upon receipt of acomparator device output signal as illustrated in FIG. 5, theoperational amplifier will be operative to generate at the base oftransistor 109 an output voltage which will either be graduallyincreasing in the case of a negative input signal from comparator 40 orwill be gradually decreasing in the case of a positive input from thecomparator 40 so as to add or subtract incremental units of base drivefor transistor 109. This will result in increasing or decreasing themagnitude of the current I and hencelchanging the slope of the rampvoltage generatedat the capacitor 103, 104 receiving this current.

Again with referenceto FIG. 6, this will result in a curve identified as4b for decreasing values of current I and the curve 4a for increasingvalues of 1 For convenience, the deviations between curves 4a, 4b, and 4have been greatly exaggerated. With reference now to FIG. 7, the circuitof FIG. 3 and the curve 4a would generate a fuel injection command pulsehaving a duration from T to T while the curve 4 would generate a fuelinjection command pulse having a duration from T, to T and the curve 4bwould generate the fuel injection command pulse subsisting from time T,to T It can thus be seen, that for a givenset of operating conditionsfor the engine, exemplified by the fact that threshold curve 5 in FIG. 4is unchanging, the quantity of fuel delivered to the engine'may bevaried by the closed loop control system of the present'invention tomaintain the air/fuel ratio at the predetermined value.

It will be seen that the present invention accomplishes its statedobjectives. By providinga comparator responsive to the sensor with fixedmaximum and minimum values,- and switchable therebetween in response tosensor signal excursions through the selected transitional value, thecharacteristic of the closed loop control signal applied to the fueldelivery controller is rendered independent of variation in thecharacteristic of the sensor signal so that the fuel delivery controllerresponse is uniform and will only respond to variations in engineperformance with respect to the set point.

I claim: v

1. An internal combustion engine control system for modulating an engineoperating parameter substantially independently of environmentallyinduced sensor I output variations,-sai d control system comprising:

sensor means forexamining an engine operating variable operative -togenerate a sensor means signal having an environmentally variablecharacteristic selected to be indicative of a quality of the combustionprocess occurring within the engine said variable characteristic beingsubject to environmentally induced variations; comparator meansresponsive to the sensor means signal operative to generate a comparatormeans output signal having a predetermined constant level signalestablished when said combustion process quality is one of a greater orlesser quality than a predetermined quality;

integrator means receiving said comparator output signal operative tointegrate said predetermined constant signal level to generate agradually changing output signal changing in one of two changedirections at a predetermined integrating rate as long as saidpredetermined constant level signal is established; and

fuel delivery controller means receiving said gradually changing outputsignal and operative to modulate fuel delivery in response thereto;

whereby said predetermined constant level signal and said predeterminedintegrating rate cause said fuel delivery modulation to be substantiallyindependent of said environmentally induced variations in said sensorcharacteristic.

2. The system as claimed in claim 1 wherein said sensor means signalvariable characteristic varies with air/fuel ratio and comprises atransitional band portion intermediate a relatively high strength signaland a relatively low strength signal, said transitional band portionbeing constant with variations in said high and low strength signalsinduced by variations of at least one environmental condition; andoccurring substantially at a selected air/fuel ratio;

wherein said systemcomprises reference level establishing meansoperative to provide said comparator means with a set point level withinsaid sensor transitional band portion indicative of saidpredeterminedquality; wherein said comparator means output signal comprises a secondconstant signal level different from said predetermined constant levelsignal, said second constant level signal being established as long assaid quality deviation is the other of said greater and lesserqualities; wherein said integrator means integrates said second constantsignal level to gradually'change said gradt ually changing signal levelin the other of said two changes directions at said predeterminedintegrating rates; and wherein said fuel delivery controller meansmodulatesfuel delivery so as to gradually increase the air/fuel ratiowhen said comparator output signal is established atv one of saidpredetermined and second constant levels signals and to otherwisegradually decrease said air/fuel ratio when said comparator outputsignal is established at the other of said predeterminedv and secondconstant levels signals;

whereby said predetermined integrating rate and the difference betweensaid predetermined and second constant signal levels causes saidfueldelivery controller to vary the air/fuel ratio about said selectedair/fuel ratio within a range of air/fuel ratios substantially,independent of said variation of said at least one environmentalcondition.

3. The system as claimed in claim 1 wherein said fuel deliverycontroller means comprises atleast one timing capacitor and currentsource means controllable to selectively charge said timing capacitor ata controllable rate from an initial value determined in accordance witha second engine operating variable to a threshold value determine inaccordance with a third engine operating variable, said controllablerate being varied in accordance with said gradually changing output.signal to controllably modulate the quantities of fuel delivered to theassociated engine independently of variations in fuel delivery commandedto accommodate changes in said second and third operating variables.

4. The system as claimed in claim 1 wherein said integrator measncomprises an operational amplifier having an input terminal and anoutput terminal and an integrating capacitor coupling said inputterminal and output terminal and determining asid predeterminedintegrating rate.

5. The system as claimed in claim 2 wherein said relatively highstrength signal level comprises a minimum high strength signal level andsaid relatively low strength sensor signal level comprises a maximum lowstrength signal level, said minimum high strength signal level and saidmaximum low strength signal level each varying with the temperature andaging characteristics of said sensor means and the difference betweenminimum high strength and maximum lower strength signal levels definingsaid constant transitional band so as to be substantially independent ofthe aging and temperature characteristics of said sensor means so thatthe fuel delivery controller means modulates fuel delivery sub- 10 vstantially independent of the aging and temperature characteristics ofsaid sensor means.

6. The system as claimed in claim 4 wherein said comparator meanscomprises an operational amplifier having an input terminal and anoutput terminal coupled by parallelly connected oppositely polledsemiconductor current conducting devices each having a predeterminedvoltage drop when conducting, said predetermined voltage dropsestablishing the magnitude-of said constant signal levels and permittingsaid comparator means to switch substantially instantaneously from oneof said constant signal levels to the other when said sensor meanssignal passes through said set point level so that the range in whichsaid sensor means signal varies about said set point level is determinedsubstantially by said magnitudes of said constant signal levels and saidpredetermined rate at which said integrator means integrates saidcomparator output signals. 7

7. An internal combustion engine controlling an engine parameter varyingwith operating conditions of an, internal combustion engine, saidcontrolsystem comprising:

a. sensor means operatively connected with said engine to provide asensor means signal having a range of values varying with said engineparameter;

b. reference level establishing means for providing a set point levelwithin said range of said sensor means signal;

c. comparator means connected to receive said sensor means signalandsaid set point level operative to establish one of a constant positiveand negative polarity comparator output signal when saidv sensor meanssignal is greater than said set'point level and to establish the otherof said constant positive and negative polarity comparator outputsignals when said sensor means signal is less than said set point level;

d. integrator means operatively connected with said comparator means togenerate a control signal having a magnitude changing with the integralof said constant positive polarity comparator output signal when saidconstant positive polarity comparator output signal is established andwith the integral of said constant negative polarity comparator outputsignal when said constant negative polarity comparator output signal isestablished; and

e. control means operatively connecting said integrator means and saidengine for controlling said engine to vary said engine parameter inaccordance with said control signal,

whereby the integration of said constant positive and negative polaritycomparator output signals causes said control signal to control saidengine so as to vary said engine parameter so that said sensor meanssignal is alternately increased and decreased through said set pointlevel.

8. The engine control system of claim 7 wherein said comparator meanscomprises an operational amplifier having an input terminal and anoutput terminal coupled by parallelly connected oppositely polledsemiconductor current conducting devices each having a predeterminedvoltage drop when conducting, said predetermined voltage dropsestablishing the magnitudes of said constant output signals andpermitting said comparator means to switch substantially instantaneouslyfrom one of said constant positive and negative output 1 l signals tothe other when said sensor means signal passes through said set pointlevel so that said range in which said sensor means signal varies aboutsaid set point level is determined substantially by said magnitudes ofsaid constant positive and negative polarity comparator output signalsand the rate at which said integrator means integrates said comparatoroutput signals 9. The apparatus of claim 8 wherein said semiconductordevices comprise forward drops of said unidirectional current conductingdevices having nominal forward voltage drops establishing said constantoutput signals.

10. The apparatus of claim 7 wherein said control means comprises anoperator controllable air/fuel delivery means for deliveringcontrollable air/fuel mixture to the engine, said control meansoperative to control one of said airand fuel so as to vary the air/fuelratio in a predetermined range about a selected air/fuel ratio. 1

11. An internal combustion engine control system for modulating anengine operating parameter substantially independently ofenvironmentally induced sensor output variations, said control systemcomprising:

sensor means for examining an engine operating variable operative togenerate a sensor means signal having an environmentally variablecharacteristic selected to be indicative of a quality of the combustionprocess occurring within the engine said vari- 12 able characteristicbeing subject to environmentally induced variations;

reference level establishing means for generating a set point levelhaving a value in the range of. values of said sensor means signal; I

comparator means connected to said sensor means and said reference levelestablishing means operative to provide a comparator signal having firstand second constant magnitudes when said sensor means signal isrespectively above and below said set point level;

integrator means operatively connected with said comparator meansoperative to generate a control signal having a magnitude changing at afirst predetermined integrating rate when the magnitude of saidcomparator signal is one of said first and second constant magnitudesand a second predeter- 1 mined integrating rate when the magnitude ofsaid comparison signal is the other of said first and second constantmagnitudes;

fuel delivery controller means receiving said gradually changing outputsignal and operative to modulate fuel delivery in response thereto;

whereby said first and second constant levels and said predeterminedintegrating rate cause said fuel delivery modulation to be substantiallyindependent of said environmentally induced variations in said sensorcharacteristic.

- UNITED STATES PATENT OFFICE CERTIFICATE ()F CORREC'IION Patent No. 33361 Dated June 1] 1974 Inventor(s) l William R. Seitz It is certifiedthat error appears in the above-identified patent ,and that said LettersPatent are hereby corrected as shown below:

' IN THE SPECIFICATION Column 1 Line 64 after "Context" deiete Column 2,Line 22 after "sensor" insert IN THE CLAIMS Claim 2, Column 9, 'Line l7delete the word "changes" and insert therefor ---change---; v

delete the word "measn" and insert therefor Claim 4, Column 9-, Line 50---means---;

Claim 4,'Column Line 53 delete "asid" and insert therefor said---;

Claim 5, Column 9, Line 63 delete "lower" and insert therefor ---low---;

Claim 7 Column l0, Line 19- after "engine" insert ---control systemfor---.

Signed-and sealed this 1st day of October 1974.

(SEAL) Attest: I

MCCOY M. GIBSON JR. 0. MARSHALL DANN Attesting Officer Commissioner ofPatents 3 U.S. GOVERNMENT PRINTING OFFICE Ill 0-366-33 RM Po-105O(10459) I uscoMM-oc 60376-P69 Patent No. 3,815,561

Dated June 1] 1974 Inventor(s) It is certified that error appears in theabove-identified patent and that said Letters Patent are herebycorrected as shown below:

NiHiam R. Seitz IN THE SPECIFICATION Column 1 Line 64 Coiumn 2, Line 22after "context" deiete "3 after "sensor" insert IN THE CLAIMS Ciaim 2',COMM 9, Line 17 Ciaim 4,

Coiumn 9, Line 50 Ciaim 4, Column 9, Line 53 Ciaim 5, Coiumn 9,- Line 63Ciaim 7, Coiumn 10, Line 19- for---.

Signed and sealed this 1st day of October 1974.

(SEAL) Attest:

MCCOY M. GIBSON JR. Attesting Officer RM PC3-1050 (10-69) C. MARSHALLDANN Commissioner of Patents USCOMM-DC 60370-P69 fi U.S. GOVERNMENTPRINTING OFF CE: l9. 0-366-334

1. An internal combustion engine control system for modulating an engineoperating parameter substantially independently of environmentallyinduced sensor output variations, said control system comprising: sensormeans for examining an engine operating variable operative to generate asensor means signal having an environmentally variable characteristicselected to be indicative of a quality of the combustion processoccurring within the engine said variable characteristic being subjectto environmentally induced variations; comparator means responsive tothe sensor means signal operative to generate a comparator means outputsignal having a predetermined constant level signal established whensaid combustion process quality is one of a greater or lesser qualitythan a predetermined quality; integrator means receiving said comparatoroutput signal operative to integrate said predetermined constant signallevel to generate a gradually changing output signal changing in one oftwo change directions at a predetermined integrating rate as long assaid predetermined constant level signal is established; and fueldelivery controller means receiving said gradually changing outputsignal and operative to modulate fuel delivery in response thereto;whereby said predetermined constant level signal and said predeterminedintegrating rate cause said fuel delivery modulation to be substantiallyindependent of said environmentally induced variations in said sensorcharacteristic.
 2. The system as claimed in claim 1 wherein said sensormeans signal variable characteristic varies with air/fuel ratio andcomprises a transitional band portion intermediate a relatively highstrength signal and a relatively low strength signal, said transitionalband portion being constant with variations in said high and lowstrength signals induced by variations of at least one environmentalcondition; and occurring substantially at a selected air/fuel ratio;wherein said system comprises reference level establishing meansoperative to provide said comparator means with a set point level withinsaid sensor transitional band portion indicative of said predeterminedquality; wherein said comparator means output signal comprises a secondconstant signal level different from said predetermined constant levelsignal, said second constant level signal being established as long assaid quality deviation is the other of said greater and lesserqualities; wherein said integrator means integrates said second constantsignal level to gradually change said gradually changing signal level inthe other of said two changes directions at said predeterminedintegrating rates; and wherein said fuel delivery controller meansmodulates fuel delivery so as to gradually increase the air/fuel ratiowhen said comparator output signal is established at one of saidpredetermined and second constant levels signals and to otherwisegradually decrease said air/fuel ratio when said comparator outputsignal is established at the other of said predetermined and secondconstant levels signals; whereby said predetermined integrating rate andthe difference between said predetermined and second constant signallevels causes said fuel delivery controller to vary the air/fuel ratioabout said selected air/fuel ratio within a range of air/fuel ratiossubstantially independent of said variation of said at least oneenvironmental condition.
 3. The system as claimed in claim 1 whereinsaid fuel delivery controller means comprises at least one timingcapacitor and current source means controllable to selectively chargesaid timing capacitor at a controllable rate from an initial valuedetermined in accordance with a second engine operating variable to athreshold value determine in accordance with a third engine operatingvariable, said controllable rate being varied in accordance with saidgradually changing output signal to controllaBly modulate the quantitiesof fuel delivered to the associated engine independently of variationsin fuel delivery commanded to accommodate changes in said second andthird operating variables.
 4. The system as claimed in claim 1 whereinsaid integrator measn comprises an operational amplifier having an inputterminal and an output terminal and an integrating capacitor couplingsaid input terminal and output terminal and determining asidpredetermined integrating rate.
 5. The system as claimed in claim 2wherein said relatively high strength signal level comprises a minimumhigh strength signal level and said relatively low strength sensorsignal level comprises a maximum low strength signal level, said minimumhigh strength signal level and said maximum low strength signal leveleach varying with the temperature and aging characteristics of saidsensor means and the difference between minimum high strength andmaximum lower strength signal levels defining said constant transitionalband so as to be substantially independent of the aging and temperaturecharacteristics of said sensor means so that the fuel deliverycontroller means modulates fuel delivery substantially independent ofthe aging and temperature characteristics of said sensor means.
 6. Thesystem as claimed in claim 4 wherein said comparator means comprises anoperational amplifier having an input terminal and an output terminalcoupled by parallelly connected oppositely polled semiconductor currentconducting devices each having a predetermined voltage drop whenconducting, said predetermined voltage drops establishing the magnitudeof said constant signal levels and permitting said comparator means toswitch substantially instantaneously from one of said constant signallevels to the other when said sensor means signal passes through saidset point level so that the range in which said sensor means signalvaries about said set point level is determined substantially by saidmagnitudes of said constant signal levels and said predetermined rate atwhich said integrator means integrates said comparator output signals.7. An internal combustion engine controlling an engine parameter varyingwith operating conditions of an internal combustion engine, said controlsystem comprising: a. sensor means operatively connected with saidengine to provide a sensor means signal having a range of values varyingwith said engine parameter; b. reference level establishing means forproviding a set point level within said range of said sensor meanssignal; c. comparator means connected to receive said sensor meanssignal and said set point level operative to establish one of a constantpositive and negative polarity comparator output signal when said sensormeans signal is greater than said set point level and to establish theother of said constant positive and negative polarity comparator outputsignals when said sensor means signal is less than said set point level;d. integrator means operatively connected with said comparator means togenerate a control signal having a magnitude changing with the integralof said constant positive polarity comparator output signal when saidconstant positive polarity comparator output signal is established andwith the integral of said constant negative polarity comparator outputsignal when said constant negative polarity comparator output signal isestablished; and e. control means operatively connecting said integratormeans and said engine for controlling said engine to vary said engineparameter in accordance with said control signal, whereby theintegration of said constant positive and negative polarity comparatoroutput signals causes said control signal to control said engine so asto vary said engine parameter so that said sensor means signal isalternately increased and decreased through said set point level.
 8. Theengine control system of claim 7 wherein said comparator means comprisesan operational amplifier having An input terminal and an output terminalcoupled by parallelly connected oppositely polled semiconductor currentconducting devices each having a predetermined voltage drop whenconducting, said predetermined voltage drops establishing the magnitudesof said constant output signals and permitting said comparator means toswitch substantially instantaneously from one of said constant positiveand negative output signals to the other when said sensor means signalpasses through said set point level so that said range in which saidsensor means signal varies about said set point level is determinedsubstantially by said magnitudes of said constant positive and negativepolarity comparator output signals and the rate at which said integratormeans integrates said comparator output signals.
 9. The apparatus ofclaim 8 wherein said semiconductor devices comprise forward drops ofsaid unidirectional current conducting devices having nominal forwardvoltage drops establishing said constant output signals.
 10. Theapparatus of claim 7 wherein said control means comprises an operatorcontrollable air/fuel delivery means for delivering controllableair/fuel mixture to the engine, said control means operative to controlone of said air and fuel so as to vary the air/fuel ratio in apredetermined range about a selected air/fuel ratio.
 11. An internalcombustion engine control system for modulating an engine operatingparameter substantially independently of environmentally induced sensoroutput variations, said control system comprising: sensor means forexamining an engine operating variable operative to generate a sensormeans signal having an environmentally variable characteristic selectedto be indicative of a quality of the combustion process occurring withinthe engine said variable characteristic being subject to environmentallyinduced variations; reference level establishing means for generating aset point level having a value in the range of values of said sensormeans signal; comparator means connected to said sensor means and saidreference level establishing means operative to provide a comparatorsignal having first and second constant magnitudes when said sensormeans signal is respectively above and below said set point level;integrator means operatively connected with said comparator meansoperative to generate a control signal having a magnitude changing at afirst predetermined integrating rate when the magnitude of saidcomparator signal is one of said first and second constant magnitudesand a second predetermined integrating rate when the magnitude of saidcomparison signal is the other of said first and second constantmagnitudes; fuel delivery controller means receiving said graduallychanging output signal and operative to modulate fuel delivery inresponse thereto; whereby said first and second constant levels and saidpredetermined integrating rate cause said fuel delivery modulation to besubstantially independent of said environmentally induced variations insaid sensor characteristic.